Disable Safe Sleep

Mac portables can become un-bootable off their hard drive if the safe-sleep image is corrupted.

See for further information (partially extracted below):

http://www.macosxhints.com/article.php?story=20070302210328928

and for even more / better information:

http://www.macfixit.com/article.php?story=20090730194723909

Newer portable Macs use safe sleep (hibernation) in combination with normal sleep (older computers can use this, too). What happens is that when you put your computer to sleep, the system writes the contents of RAM into the file /private/var/vm/sleepimage, then goes into normal sleep mode. If your system loses power completely, it can recover the contents of RAM from this sleepimage file.

The problem with this is putting your computer to sleep can take a while (20 seconds to one minute or more), depending on how much data you currently have loaded in RAM. Also, this sleepimage file is the same size of your total RAM, wasting valuable hard drive space. I have 2GB of RAM, so my file is 2GB.

To disable safe sleep, run the two following commands in Terminal:

$ sudo pmset -a hibernatemode 0
$ sudo nvram "use-nvramrc?"=false

When done, restart your computer. Now go delete the file /private/var/vm/sleepimage" to free up some hard drive space.